Positron Decay ofY88

The weak positron spectrum in the decay of ${\mathrm{Y}}^{88}$ has been investigated using a $4\pi$-positron-scintillation spectrometer. Two measurements of the spectrum yield experimental shape factors which are consistent above 250 keV with that expected for a unique once-forbidden transition. The average end-point energy obtained in these two measurements is 761±9 keV. The positron branching was measured and found to be 0.20±0.01%. The $log\mathrm{ft}$ is 9.4, and $log{f}_{1}t$ is 8.7. On the basis of recent measurements of the gamma-ray intensities in the ${\mathrm{Y}}^{88}$ decay the electron capture branching to the 1840-keV level is determined to be 5.8±0.7%, which yields an electron capture to positron ratio of 29±4 for this transition.